Tectonic evolution and continental crust growth of Northern Xinjiang in northwestern China: Remnant ocean model

• Published in: Earth-science reviews 2013-11, Vol.126, p.178-205
• Main Authors: Xu, Qin-Qin, Ji, Jian-Qing, Zhao, Lei, Gong, Jun-Feng, Zhou, Jing, He, Guo-Qi, Zhong, Da-Lai, Wang, Jin-Duo, Griffiths, Lee
• Format: Article
• Language: English
• Subjects: Basalt; Continental crust growth; Crusts; deformation; Dikes; Evolution; Geochemistry; Granite; gravity; Isotopes; Magma; marine sediments; mass transfer; melting; Northern Xinjiang; Ocean models; Oceans; Ophiolite; Plate tectonics; Remnant ocean; Rock deformation; Rocks; sediment deposition; Sedimentary geology; Tectonics
• ISSN: 0012-8252; 1872-6828
• DOI: 10.1016/j.earscirev.2013.08.005

The Northern Xinjiang region is located in the southwestern part of the Central Asian Orogenic Belt (CAOB, also known as the Altaid Tectonic Collage). Despite extensive research aimed at understanding the crustal growth of the CAOB and the evolution of the Paleo-Asian Ocean, the tectonic evolution mechanism of continental crust growth in Northern Xinjiang remains controversial. The geology of Northern Xinjiang is characterized by widespread ophiolites, granitoids, intermediate–basic dikes. Most of the ophiolites were generated in the early Paleozoic. The ophiolites are widely spread around the Junggar Basin, but their distribution does not indicate a well-defined band. Their outcrops are generally related to various faults. The basic rocks widespread in Northern Xinjiang are grouped into two categories: (i) gabbros, diabases basalts of the ophiolites and (ii) basic dikes that intrude into the Paleozoic strata granite plutons. The basic rocks associated with the early Paleozoic ophiolites were reworked by later geothermal events with a peak 40Ar/39Ar age of 310–290Ma. The basic dikes intruded into Paleozoic strata and granite plutons during the Carboniferous–Jurassic, displaying three peaks of emplacement at 260–250Ma, 220Ma, and 200–190Ma. These two types of basic rocks and the documented Variscan magmatic rocks were derived from the same source. Their isotope geochemical characteristics and widespread distribution suggest that since the Paleozoic, a large geochemical province has existed in Northern Xinjiang with an affinity to mid-ocean ridge basalts (MORB) and ocean island basalts (OIB), which is related to a long-lived remnant ocean and the underlying early Paleozoic oceanic crust. The existence of remnant oceanic crust in Northern Xinjiang was confirmed by seismic, gravity and aeromagnetic data. Therefore, we propose the following remnant ocean model for the Paleozoic tectonic evolution of Northern Xinjiang. It consists of three stages: 1) oceanic crust formation and deposition of the overlying volcanic-sedimentary rocks during the early Paleozoic; 2) retaining of the remnant ocean with marine sediments deposited during the early stage of the late Paleozoic; and 3) widespread and pervasive emplacement of Variscan granites, intermediate–basic dikes, and their volcanic equivalents during the Late Carboniferous and Early Permian, and termination of marine sedimentation at the end of the Early Permian. The tectonic evolution of Northern Xinjiang has been